The present invention relates to balloons for angioplasty procedures and to methods of making the same.
Balloon catheters are well-known devices in which the catheter carries an inflatable balloon to occlude and seal a body space, to expand a blood vessel through pressurized inflation of the balloon, or for any other desired purpose which may typically but not necessarily be a therapeutic purpose in the medical field. In the case of dilatation balloon catheters for angioplasty, for example a PTCA procedure, the catheter balloon is generally made out of a thin, strong material which is of relatively low resilience. For example, the catheter balloon may be made out of biaxially oriented polyethylene terephthalate (PET) or a polyamide material such as nylon. Such strong, flexible materials are commonly used for angioplasty balloons, and have the advantage that they are flexible but inelastic so that they can expand outwardly to a predetermined diameter, and then cease further expansion at normal pressures, to avoid damage to the artery wall by over expansion.
Balloon formation typically involves three major steps in the process which include forming a tubular preform by extruding, injection molding dip-molding, spraying, and so forth, molding the balloon and annealing the balloon. Depending on the balloon material employed, the preform may be axially stretched before it is blown. This biaxial orientation of the material is done during the tubing expansion step. A pulling tension may or may not be employed simultaneously during the expansion step.
In a conventional balloon molding step, a tube is heated from its outside surface through the use of hot water, a heating block, or an infrared heating source, for example. Once the tube is heated to the proper balloon forming temperature beyond the softening temperature of the polymer, the balloon is then formed using pressurized air and tension.
Using the heating sources described above, however, heating gradients are created from the outside surface of the balloon where the temperature is higher, to the inside surface of the balloon where the temperature is lower. This can result in a scenario wherein the outside surface gets overheated and the inside surface is under heated. The result of such uneven heating along the cross-section of the balloon can result in premature forming and more defects, or less than optimal biaxial orientation which may be reflected in the physical characteristics of the balloon, for example, lower burst pressure and higher distention.
It is known to use induction heating technologies to weld, forge, bond or set polymer materials by mixing ferromagnetic particles in the polymer to be heated.
See for example, U.S. Pat. No. 6,056,844, which is incorporated by reference herein in its entirety.
There remains a need in the art for a balloon forming method which results in even heating of the tube during the balloon molding process which avoids detriment to the balloon characteristics.